1. Field of the Invention
The present invention relates to a scheduling control system and a method thereof, and more particularly to a wireless network scheduling control system and a method thereof, which are capable of achieving power saving with data registration and reorganization technology in a multipoint wireless transmission network, and especially suitable for a WiMAX network.
2. Related Art
With the maturity of wireless technologies, it is not limited to utilizing physical lines when constructing a network. For example, Wireless Local Area Network (WLAN) is a local area network constructed according to IEEE 802.11 communication protocol and specifications complied by Institute of Electrical and Electronic Engineer (IEEE). IEEE 802.11 is a protocol on the basis of radio technology. A WLAN constructed according to this protocol is not limited to using physical lines when forming the network, but instead, computers or communication devices can form and use the network, as long as they fall in the scope covered by radio signals. Similar wireless network includes Wireless Personal Area Network (WPAN) constructed with Bluetooth technology, Sensor Network formed by sensors, and Wireless Metropolitan Area Network (WMAN) constructed according to IEEE 802.16 protocol and specifications (or Worldwide Interoperability for Microwave Access, WiMAX). These networks constructed through wireless technologies all have the advantages that no physical lines are required; the network constructing cost is reduced, and it is not limited by the positions of physical lines.
Among others, WiMAX, a new wireless technology, has the advantages of a long transmission distance, a high transmission speed, and a low network construction cost. WiMAX has the working frequency of 2 GHz to 11 GHz, the transmission distance of up to 50 km, and supports the network structure of Point to Point (P2P) or Point to Multi-Point (PMP). Moreover, WiMAX can select to operate at the frequency between 2 GHz and 11 GHz according to the requirements on service levels. As for the PMP operating mode of WiMAX, data is directly transmitted between a node playing the role of a base station (BS) and a subscriber station (SS) or a mobile station (MS) playing the role of an end receiving/transmitting node. In order to perform the data transmission, connections must be established before the data transmission happens. Each connection has a connection ID (CID). The same CID is corresponding to the same service flow, and the same service flow is corresponding to the same quality of service (QoS) parameters. Under Mobile Multi-hop Relay (WiMAX MMR) network architecture, besides the BS and SS/MS, one or more relay nodes playing the role of relay stations can be used to expand the transmission scope of the BS, or enhance the overall transmission rate. According to the description on relay specifications in IEEE 802.16j, under a time division duplex (TDD) mode, a frame can be divided into a plurality of zones according to the transmission time. These zones have different functions, for example, a zone that transmits data to and receives data from an end receiving/transmitting node is referred as an access zone, and a zone that transmits data to and receives data from a relay node is referred as a relay zone. Moreover, the zones can also be classified into uplink zone (UL-Zones) and downlink zones (DL-Zones). Herein, the downlink refers to the transmission direction from BS to SS/MS, including the transmission from BS to RS or SS/MS, or the transmission from RS to SS/MS, or the transmission from RS downwards to RS; the uplink refers to the transmission direction from SS/MS to BS, including the transmission from SS/MS to BS, or the transmission from SS/MS to RS, or the transmission from RS upwards to RS or BS. Each of the zones includes a plurality of data bursts. In a downlink transmission, a pack of MAC Protocol Data Units (MAC PDUs) is included in the data bursts, which is generally transmitted to a certain SS/MS. However, under the circumstances of multicast or broadcast, the MAC PDUs may be sent to a number of SS/MS. If the MAC PDUs must be sent to a number of SS/MS, CIDs in headers (e.g., generic MAC header, GMH) of the pack of MAC PDUs have to be the same. In an uplink transmission, a pack of MAC PUDs in the same data burst is from the same SS/MS. As for uplink data, the SS/MS or RS will combine the transmitted data into one or more data bursts, and request BS or RS to arrange a period for the SS/MS or RS to transmit the bursts in the schedule. As for downlink data, the BS or RS will also combine the transmitted data into one or more data bursts, allocate a period to transmit the bursts in the schedule. As described above, the data is transmitted via frames in the MAC. Before the data is received and transmitted, the allocated schedule will be prepared in an MAP of a frame, and the MAP will be broadcasted when the frame starts. The MAPs are classified into uplink MAPs (UL-MAPs) and downlink MAPs (DL-MAPs). All the devices in the network (e.g., BS, RS, and SS/MS) will receive the data with appropriate modulation and codes at an appropriate start time point according to planned instructions in the DL-MAPs, and will transmit the data with appropriate modulation and codes at an appropriate start time point according to planned instructions in the UL-MAPs. In other words, the MAPs specify the sequence, start time, and duration for the data transmission of BS, RS, and SS/MS.
Generally, if an end receiving/transmitting node in a wireless network is a mobile device, such as an MS of WiMAX or an MS of WLAN (e.g., a notebook, PC, or PDA), the power is often supplied by a secondary battery. Once the power of the battery is run out, the MS cannot perform the data transmission. In a multiple-access wireless network in which the data transmission and the scheduling control are separated, a transmitted frame generally includes data of a number of nodes at the same time. As for a specific end receiving/transmitting node, if only a short period of transmission duration among the whole transmission duration of the frame is planned for the end receiving/transmitting node to receive and transmit the data in a frame according to the scheduling plan, during the transmission of this frame, the time in which no data is transmitted for the end receiving/transmitting node is a waste of power from the perspective of said end node. To an end receiving/transmitting node, the power saving mechanism is generally realized via the node entering a sleeping mode. For WiMAX, instead of transmitting data in a competitive mode as in WLAN, the network characteristic is a multiple-access wireless network in which the data transmission and the scheduling control are separated from each other. In WiMAX, the end receiving/transmitting node MS is instructed to enter the sleeping mode at an appropriate time through a control message by BS, and the minimum unit for entering the sleeping mode each time is one frame. In the WiMAX network, if the control scheduling DL-MAP or UL-MAP of a certain frame plans that the MS needs to participate in data receiving or transmission in a specific frame, the MS cannot enter the sleeping mode to save the power during the transmission of this period. On the contrary, if the control scheduling DL-MAP or UL-MAP plans that the MS does not need to participate in data receiving or transmission in a specific frame, the MS can enter the sleeping mode to save the power during the transmission of this frame. Therefore, if the frame structure is well planned to increase the opportunity that the MS enters the sleeping mode, the MS will save the precious power. For example, FIG. 1 is a schematic view of the frame structure of WiMAX Mobile Multi-hop Relay (WiMAX MMR). Referring to FIG. 1, it is assumed that the network includes a BS, an RS, and three MSs (MS1 to 3). A preamble 110 of a frame 100 is used for detecting devices in the WiMAX network (BS, RS, and MS) and performing time synchronization, and the like. A MAP 120 includes a UL-MAP and a DL-MAP, for planning transmission schedules for devices participating in the data transmission. The rest part of the frame 100 excluding the preamble 110 and the MAP 120 is further divided into a zone 130 and a zone 140. The zone 130 includes three downlink data burst sets 131 to 133 (i.e., the sets of data bursts), and the zone 140 includes uplink data burst sets. It is assumed that in the DL-zone 130, the data burst set 131 is transmitted from BS to RS, the data burst set 132 is transmitted from RS to MS1, and the data burst set 133 is transmitted from RS to MS2, and the zone 140 does not include any uplink scheduling plan of MS1, MS2, and MS3. In this example, only MS3 can enter the sleeping mode as it does not participate in the uplink and downlink transmission, while MS1 and MS2 cannot enter the sleeping mode. Though MS1 and MS2 do not participate in the transmission during the uplink of the frame 140, MS1 and MS2 still have to remain in the active mode that consumes a high power, and cannot enter the sleeping mode, owing to the aforementioned power saving limit (i.e., the minimum unit for entering the sleeping mode each time is one frame). In other words, during the transmission of this frame, which includes a number of data burst sets, even if only a small part of the data burst sets are related to MS1 or MS2 according to the MAP planning, MS1 and MS2 cannot enter the sleeping mode during the whole transmission period of this frame.
Currently, the power saving mechanism exercised in WiMAX mainly involves enabling an MS to enter the power saving mode through coordination between its associated BS and the MS. In a WiMAX MMR network, data transmission between BS and MS can be relayed by one or more intermediate transmission nodes, RS(s). The present invention will provide a mechanism that registers data at intermediate transmission nodes RS and reorganizes data in a transmitted frame structure by re-planning MAP, such that a specific end receiving/transmitting node MS can receive and send relevant data as collectively as possible, so as to increase the opportunities for the MS to enter sleep mode to achieve the objective of saving power and prolonging the operation time.